The subject matter disclosed herein relates generally to nuclear medicine (NM) imaging systems and techniques, such as single-photon emission computed tomography (SPECT) or positron emission tomography (PET).
NM imaging is generally based on measurement of radiopharmaceutical distribution in a patient's body. A radiopharmaceutical, for example, may be injected into the blood vessels of a patient and be physiologically distributed via blood flow in the entire body of the patient. Generally, the radiopharmaceutical uptake in imaged organs is time limited, and the complete uptake from circulated blood may take from a few seconds to several hours, depending on the pharmaceutical used.
The image quality of the imaged organs is directly proportional to the absolute radio-activity uptake value (or volume concentration) in the imaged organ or tissue. The higher the absolute radio-activity uptake, the better the image quality of the imaged organ or tissue. Image quality may also increased by longer imaging time. However, prolonging the imaging time may cause patient discomfort and reduce throughput of the imaging facility, as well as increase risk of blurring due to patient motion. The absolute radio-activity uptake in imaged organs or tissue is conventionally controlled by injection dose (in terms of absolute volume and/or radio-activity concentration) for the given radiopharmaceutical used. The injection dose of radio-activity is distributed inside the patient body and causes radiation exposure to the patient's organs and tissue until the radiopharmaceutical is reduced to negligible activity, for example, due to physical causes (e.g., half-life or deterioration of the radionuclide) and physiological causes (e.g., wash-out via excretion from the patient body). Generally, the higher the injection dose of radio-activity, the higher the total effective radiation dose of the imaged patient. However, because the radiation dose is administered or distributed to the entire patient body and because only a portion of the patient is imaged, the patient is subjected to higher radiation doses than would otherwise be necessary if radiation were limited to the organ(s) or tissue to be imaged.